Trump to North Korea: Be very, very nervous

President Donald Trump has warned North Korea it should be very, very nervous if it does anything to the US.
He said the regime would be in trouble like few nations have ever been if they do not get their act together .
His comments came after Pyongyang announced it had a plan to fire four missiles near the US territory of Guam.
US Defence Secretary James Mattis warned that armed conflict with North Korea would be catastrophic and said diplomacy was bearing fruit.
The American effort is diplomatical